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Question for an expert: what distance to install PAPI

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I am a retired commercial pilot who enjoys playing with FSX.  Over the years I have tweaked the default AFCADs on many default airports to bring them up to current real world charts.  I use ADE 1.5 but am in no way an expert.  This is not a question about how to use ADE but rather a tactical question on the correct placement of PAPI4 lights in FSX scenery so they will appear correctly over the runway end.


1.  The default FSX airports all have PAPI4 lights set 750 feet in from the runway end lights and in most cases the default GS signal corresponds to the correct TCH per the charts.  PAPI (unlike VASI) are designed for accuracy down to touchdown and usually are set to correspond to the GS on approach (unlike VASI) and when not aligned this way it is noted on the approach charts.  Usual TCH is between 50-55 ft agl in real world.


2.  Up until a few weeks ago, all my PAPI4 in the FSX default airports seemed to be close to coinciding with the ILS GS at decision height (using the 750 ft displacement FSX default positioning) though it always seemed that they should be placed BEYOND the touchdown point since they are being observed from eye level which is 10-20 ft above the GS receiver(?)  But since they coincided correctly within FSX, it functionally was adequate for my simulated flights so I just accepted that positioning and used it when I added or tweaked runways using ADE.


3.  Recently, however, something unexplained has occurred.  Namely, the PAPI lights are now indicating a crossing height of around 25-30 ft agl and hence 20 feet below the GS glidepath over the threshold.   I have tried every model in my livery at many different default airports and the result is always the same.  I tried every adjustment and tweak of the config file along with reloading a virgin camera file, all to no avail.  Out of frustration I finally opted to uninstall everything and reinstall FSX and all my addons.  Sadly, I am still getting the same erroneous results.


4.  I can only assume that some unintended 'automatic' upgrade on my PC in the last several weeks has modified a system file.  I have tried a restore but in my VISTA home 64 SP1, my data only goes back a few days which apparently is not far enough to restore my system to BEFORE the mess-up.


5.  I am sure many (or at least some) who read this must chuckle at my problem and know exactly what is causing the anomaly.  I haven't a clue.  My question is simple:  what are you observing as a TCH on the default FSX runways on your system?  And what distance are you setting the PAPI on new scenery you are developing so that they reflect alignment with the GS?


6.  Currently with the existing problem I would have to move the PAPI to 1250-1350 feet beyond the runway end to have them agree with the published TCH on the charts!  What has been your experience?


Any (and I mean ANY!) help will be greatly appreciated. 

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